Publications

Proposed for publication in Nature Materials.

Rohwer, Lauren E.; Anderson, Robert A.

Abstract not provided.

Simmons, J.A.; Fischer, Arthur J.; Crawford, Mary H.; Abrams, B.L.; Biefeld, Robert M.; Koleske, Daniel K.; Allerman, A.A.; Figiel, J.J.; Creighton, J.R.; Coltrin, Michael E.; Tsao, Jeffrey Y.; Mitchell, Christine C.; Kerley, Thomas M.; Wang, George T.; Bogart, Katherine B.; Seager, Carleton H.; Campbell, Jonathan C.; Follstaedt, D.M.; Norman, Adam K.; Kurtz, S.R.; Wright, Alan F.; Myers, S.M.; Missert, Nancy A.; Copeland, Robert G.; Provencio, P.N.; Wilcoxon, Jess P.; Hadley, G.R.; Wendt, J.R.; Kaplar, Robert K.; Shul, Randy J.; Rohwer, Lauren E.; Tallant, David T.; Simpson, Regina L.; Moffat, Harry K.; Salinger, Andrew G.; Pawlowski, Roger P.; Emerson, John A.; Thoma, Steven T.; Cole, Phillip J.; Boyack, Kevin W.; Garcia, Marie L.; Allen, Mark S.; Burdick, Brent B.; Rahal, Nabeel R.; Monson, Mary A.; Chow, Weng W.; Waldrip, Karen E.

This SAND report is the final report on Sandia's Grand Challenge LDRD Project 27328, 'A Revolution in Lighting -- Building the Science and Technology Base for Ultra-Efficient Solid-state Lighting.' This project, which for brevity we refer to as the SSL GCLDRD, is considered one of Sandia's most successful GCLDRDs. As a result, this report reviews not only technical highlights, but also the genesis of the idea for Solid-state Lighting (SSL), the initiation of the SSL GCLDRD, and the goals, scope, success metrics, and evolution of the SSL GCLDRD over the course of its life. One way in which the SSL GCLDRD was different from other GCLDRDs was that it coincided with a larger effort by the SSL community - primarily industrial companies investing in SSL, but also universities, trade organizations, and other Department of Energy (DOE) national laboratories - to support a national initiative in SSL R&D. Sandia was a major player in publicizing the tremendous energy savings potential of SSL, and in helping to develop, unify and support community consensus for such an initiative. Hence, our activities in this area, discussed in Chapter 6, were substantial: white papers; SSL technology workshops and roadmaps; support for the Optoelectronics Industry Development Association (OIDA), DOE and Senator Bingaman's office; extensive public relations and media activities; and a worldwide SSL community website. Many science and technology advances and breakthroughs were also enabled under this GCLDRD, resulting in: 55 publications; 124 presentations; 10 book chapters and reports; 5 U.S. patent applications including 1 already issued; and 14 patent disclosures not yet applied for. Twenty-six invited talks were given, at prestigious venues such as the American Physical Society Meeting, the Materials Research Society Meeting, the AVS International Symposium, and the Electrochemical Society Meeting. This report contains a summary of these science and technology advances and breakthroughs, with Chapters 1-5 devoted to the five technical task areas: 1 Fundamental Materials Physics; 2 111-Nitride Growth Chemistry and Substrate Physics; 3 111-Nitride MOCVD Reactor Design and In-Situ Monitoring; 4 Advanced Light-Emitting Devices; and 5 Phosphors and Encapsulants. Chapter 7 (Appendix A) contains a listing of publications, presentations, and patents. Finally, the SSL GCLDRD resulted in numerous actual and pending follow-on programs for Sandia, including multiple grants from DOE and the Defense Advanced Research Projects Agency (DARPA), and Cooperative Research and Development Agreements (CRADAs) with SSL companies. Many of these follow-on programs arose out of contacts developed through our External Advisory Committee (EAC). In h s and other ways, the EAC played a very important role. Chapter 8 (Appendix B) contains the full (unedited) text of the EAC reviews that were held periodically during the course of the project.

Mitchell, Robert T.; Rohwer, Lauren E.; Robinson, Melissa V.; Kilgo, Riley D.; Mulhall, James M.; Fischer, Thomas A.

Abstract not provided.

Cox, Trisha D.; Sasaki, Darryl Y.; Hunter, J.A.; Jones, Gary D.; Sinclair, Michael B.; Rohwer, Lauren E.; Pohl, Phillip I.; Andrzejewski, William A.; Sasaki, Darryl Y.

An optical sensor system has been developed for the autonomous monitoring of NO{sub 2} evolution in energetic material aging studies. The system is minimally invasive, requiring only the presence of a small sensor film within the aging chamber. The sensor material is a perylene/PMMA film that is excited by a blue LED light source and the fluorescence detected with a CCD spectrometer. Detection of NO{sub 2} gas is done remotely through the glass window of the aging chamber. Irreversible reaction of NO{sub 2} with perylene, producing the non-fluorescent nitroperylene, provides the optical sensing scheme. The rate of fluorescence intensity loss over time can be modeled using a numerical solution to the coupled diffusion and a nonlinear chemical reaction problem to evaluate NO{sub 2} concentration levels. The light source, spectrometer, spectral acquisition, and data processing were controlled through a Labivew program run by a laptop PC. Due to the long times involved with materials aging studies the system was designed to turn on, warm up, acquire data, power itself off, then recycle at a specific time interval. This allowed the monitoring of aging HE material over the period of several weeks with minimal power consumption and stable LED light output. Despite inherent problems with gas leakage of the aging chamber they were able to test the sensor system in the field under an accelerated aging study of rocket propellant. They found that the propellant evolved NO{sub 2} at a rate that yielded a concentration of between 10 and 100 ppm. The sensor system further revealed that the propellant, over an aging period of 25 days, evolves NO{sub 2} with cyclic behavior between active and dormant periods.

Rohwer, Lauren E.

The past several years rendered a resurgence of interest in phosphors for low-voltage flat panel displays utilizing cathodoluminescence (CL). A major selection criterion for these phosphors is CL efficiency. The objective is to maximize the efficiency at low voltages. This work focuses on understanding the materials properties that influence CL efficiency below 1 kV. Existing high-voltage CL efficiency models take into account intrinsic materials properties such as band-gap energy. Experimental data reveals that the CL efficiency also depends on physical properties such as particle and crystallite size. An update, predictive model of CL efficiency that includes the effects of crystallite size, radiative recombination probability, and electron accelerating potential was developed. The predicted efficiencies agree very well with experimental results. The experimental data were collected using a hot filament electron gun in a demountable high-vacuum chamber. To obtain measurement accuracy, secondary electrons were collected and the phosphor excited with a uniform beam profile. A CL characterization protocol for display phosphors was established at Sandia National Laboratories and made available to phosphor researchers.

Rohwer, Lauren E.; Rohwer, Lauren E.

Fine particle porous {alpha}-alumina has been prepared by a wet chemical method of combustion synthesis using an aqueous precursor containing aluminum nitrate (oxidizer) and carbohydrazide, an organic fuel as starting materials. The aluminum nitrate and carbohydrazide were reacted exothermically at 400--600 C. The synthesis of {alpha}-alumina ({alpha}-Al{sub 2}O{sub 3}) was used as a model for understanding the effects of processing parameters on physical properties such as surface area, average pore size, and residual carbon content. The porous powders were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area analysis and elemental analysis. The decomposition of the starting materials was investigated using differential thermal and thermogravimetric analyses (DTA/TGA). It has been shown that the furnace temperature, fuel/oxidizer ratio, and precursor water content can be tailored to produce powders with different physical properties.